[iOS] Crash NSGenericException in FlutterPluginAppLifeCycleDelegate (mutation while enumeration)

### Steps to reproduce

The crash occurs in `FlutterPluginAppLifeCycleDelegate` when the `_delegates` collection is modified (a delegate is added or removed) while it is being enumerated during a lifecycle event.

This typically happens if a plugin registers or unregisters a delegate inside a callback like `application:didFinishLaunchingWithOptions:`.

Steps to reproduce logic:
1. A Flutter app starts on iOS.
2. `FlutterPluginAppLifeCycleDelegate` begins iterating over `_delegates` to forward a lifecycle event.
3. Inside the loop, one of the delegates (or a side effect) calls `addDelegate:` or `removeDelegate:`.
4. The `_delegates` NSHashTable is mutated.
5. The loop continues and crashes with `NSGenericException` because the collection was mutated during enumeration.

this crash has been introduced with 3.38.x and this PR : https://github.com/flutter/flutter/pull/176580/changes
On line 178,

  `for (NSObject<FlutterApplicationLifeCycleDelegate>* delegate in _delegates) {` should be replaced by `  for (NSObject<FlutterApplicationLifeCycleDelegate>* delegate in [_delegates allObjects]) {`

like the original code.

I'm opening a PR with Tests accordingly and this should be fixed in a 3.38.X (we're facing more than 200k crashes everyday)

### Expected results

The app should handle delegate registration/deregistration gracefully during lifecycle events without crashing.

### Actual results

The app crashes with the following exception:
```
Fatal Exception: NSGenericException
Collection <NSHashTable: ...> was mutated while being enumerated.
Stack trace:
          Fatal Exception: NSGenericException
0  CoreFoundation                 0xc5964 __exceptionPreprocess
1  libobjc.A.dylib                0x31814 objc_exception_throw
2  CoreFoundation                 0x14e5dc +[__NSFastEnumerationEnumerator allocWithZone:]
3  Flutter                        0x3d66c -[FlutterPluginAppLifeCycleDelegate application:didFinishLaunchingWithOptions:isFallbackForScene:] + 178 (FlutterPluginAppLifeCycleDelegate.mm:178)
4  Flutter                        0x3d214 -[FlutterPluginAppLifeCycleDelegate application:didFinishLaunchingWithOptions:] + 151 (FlutterPluginAppLifeCycleDelegate.mm:151)
5  Flutter                        0x13090 -[FlutterAppDelegate application:didFinishLaunchingWithOptions:] + 54 (FlutterAppDelegate.mm:54)
6  Runner                         0xcae4 AppDelegate.application(_:didFinishLaunchingWithOptions:) + 79 (AppDelegate.swift:79)
7  Runner                         0xd2f0 @objc AppDelegate.application(_:didFinishLaunchingWithOptions:) (<compiler-generated>)
8  UIKitCore                      0x1420384 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:]
9  UIKitCore                      0x1421928 -[UIApplication _callInitializationDelegatesWithActions:forScene:payload:fromOriginatingProcess:]
10 UIKitCore                      0x142594c -[UIApplication _runWithMainScene:transitionContext:completion:]
11 UIKitCore                      0xa2dce8 -[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:]
12 UIKitCore                      0xd8eb0 _UIScenePerformActionsWithLifecycleActionMask
13 UIKitCore                      0xa2e564 __101-[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]_block_invoke
14 UIKitCore                      0xa2e0d8 -[_UISceneLifecycleMultiplexer _performBlock:withApplicationOfDeactivationReasons:fromReasons:]
15 UIKitCore                      0xa2e37c -[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]
16 UIKitCore                      0xa2de08 -[_UISceneLifecycleMultiplexer uiScene:transitionedFromState:withTransitionContext:]
17 UIKitCore                      0xa39288 __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke
18 UIKitCore                      0xeabec4 +[BSAnimationSettings(UIKit) tryAnimatingWithSettings:fromCurrentState:actions:completion:]
19 UIKitCore                      0xd9cc8 _UISceneSettingsDiffActionPerformChangesWithTransitionContextAndCompletion
20 UIKitCore                      0xa38f84 -[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]
21 UIKitCore                      0x8781e4 __64-[UIScene scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke.218
22 UIKitCore                      0x877278 -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:]
23 UIKitCore                      0x877e50 -[UIScene scene:didUpdateWithDiff:transitionContext:completion:]
24 UIKitCore                      0x1424918 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:]
25 UIKitCore                      0xed4cb4 -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:]
26 FrontBoardServices             0x1e3ec __95-[FBSScene _callOutQueue_didCreateWithTransitionContext:alternativeCreationCallout:completion:]_block_invoke
27 FrontBoardServices             0x1e8a4 -[FBSScene _callOutQueue_maybeCoalesceClientSettingsUpdates:]
28 FrontBoardServices             0x1e204 -[FBSScene _callOutQueue_didCreateWithTransitionContext:alternativeCreationCallout:completion:]
29 FrontBoardServices             0x8cbcc __93-[FBSWorkspaceScenesClient _callOutQueue_sendDidCreateForScene:transitionContext:completion:]_block_invoke.349
30 FrontBoardServices             0x2bf64 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:]
31 FrontBoardServices             0x48e04 -[FBSWorkspaceScenesClient _callOutQueue_sendDidCreateForScene:transitionContext:completion:]
32 FrontBoardServices             0x4a768 __92-[FBSWorkspaceScenesClient createSceneWithIdentity:parameters:transitionContext:completion:]_block_invoke_2
33 FrontBoardServices             0x2bf64 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:]
34 libdispatch.dylib              0x1b7fc _dispatch_client_callout
35 libdispatch.dylib              0x6bb4 _dispatch_block_invoke_direct
36 BoardServices                  0x91d4 __BSSERVICEMAINRUNLOOPQUEUE_IS_CALLING_OUT_TO_A_BLOCK__
37 BoardServices                  0x9054 BSServiceMainRunLoopSourceHandler
38 CoreFoundation                 0x68f10 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
39 CoreFoundation                 0x68e84 __CFRunLoopDoSource0
40 CoreFoundation                 0x46acc __CFRunLoopDoSources0
41 CoreFoundation                 0x1d6d8 __CFRunLoopRun
42 CoreFoundation                 0x1ca6c _CFRunLoopRunSpecificWithOptions
43 GraphicsServices               0x1498 GSEventRunModal
44 UIKitCore                      0x9ddf8 -[UIApplication _run]
45 UIKitCore                      0x46e54 UIApplicationMain
46 UIKitCore                      0x172938 -[UIScrollView contentInset]
47 Runner                         0xdcf0 main (AppDelegate.swift)
48 ???                            0x193592e28 (Manquant)
```
        
...

### Code sample

This is an issue within the iOS Engine embedding (`FlutterPluginAppLifeCycleDelegate`). It cannot be reproduced with pure Dart code.

To reproduce the crash, a native plugin must add or remove a delegate while the `FlutterPluginAppLifeCycleDelegate` is iterating over its delegates (e.g., during `didFinishLaunchingWithOptions`).

Here is the Objective-C unit test logic that reproduces the `NSGenericException`:

```
// 1. Define a delegate that mutates the list during execution
@interface MutatingDelegate : NSObject <FlutterApplicationLifeCycleDelegate>
@property(nonatomic, weak) FlutterPluginAppLifeCycleDelegate* container;
@end

@implementation MutatingDelegate
- (BOOL)application:(UIApplication*)application
    didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
    // THIS CAUSES THE CRASH: Modifying the collection while it is being iterated
    [self.container addDelegate:[[NSObject alloc] init]]; 
    return YES;
}
@end

// 2. The Test Case
- (void)testCrashReproduction {
    FlutterPluginAppLifeCycleDelegate* delegate = [[FlutterPluginAppLifeCycleDelegate alloc] init];
    MutatingDelegate* mutatingDelegate = [[MutatingDelegate alloc] init];
    mutatingDelegate.container = delegate;
    
    [delegate addDelegate:mutatingDelegate];
    
    // This line throws "Fatal Exception: NSGenericException"
    // "Collection <NSHashTable> was mutated while being enumerated."
    [delegate application:[UIApplication sharedApplication]
        didFinishLaunchingWithOptions:nil];
}
```

### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

[Upload media here]

</details>


### Logs

<details open><summary>Logs</summary>

```console
          Fatal Exception: NSGenericException
0  CoreFoundation                 0xc5964 __exceptionPreprocess
1  libobjc.A.dylib                0x31814 objc_exception_throw
2  CoreFoundation                 0x14e5dc +[__NSFastEnumerationEnumerator allocWithZone:]
3  Flutter                        0x3d66c -[FlutterPluginAppLifeCycleDelegate application:didFinishLaunchingWithOptions:isFallbackForScene:] + 178 (FlutterPluginAppLifeCycleDelegate.mm:178)
4  Flutter                        0x3d214 -[FlutterPluginAppLifeCycleDelegate application:didFinishLaunchingWithOptions:] + 151 (FlutterPluginAppLifeCycleDelegate.mm:151)
5  Flutter                        0x13090 -[FlutterAppDelegate application:didFinishLaunchingWithOptions:] + 54 (FlutterAppDelegate.mm:54)
6  Runner                         0xcae4 AppDelegate.application(_:didFinishLaunchingWithOptions:) + 79 (AppDelegate.swift:79)
7  Runner                         0xd2f0 @objc AppDelegate.application(_:didFinishLaunchingWithOptions:) (<compiler-generated>)
8  UIKitCore                      0x1420384 -[UIApplication _handleDelegateCallbacksWithOptions:isSuspended:restoreState:]
9  UIKitCore                      0x1421928 -[UIApplication _callInitializationDelegatesWithActions:forScene:payload:fromOriginatingProcess:]
10 UIKitCore                      0x142594c -[UIApplication _runWithMainScene:transitionContext:completion:]
11 UIKitCore                      0xa2dce8 -[_UISceneLifecycleMultiplexer completeApplicationLaunchWithFBSScene:transitionContext:]
12 UIKitCore                      0xd8eb0 _UIScenePerformActionsWithLifecycleActionMask
13 UIKitCore                      0xa2e564 __101-[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]_block_invoke
14 UIKitCore                      0xa2e0d8 -[_UISceneLifecycleMultiplexer _performBlock:withApplicationOfDeactivationReasons:fromReasons:]
15 UIKitCore                      0xa2e37c -[_UISceneLifecycleMultiplexer _evalTransitionToSettings:fromSettings:forceExit:withTransitionStore:]
16 UIKitCore                      0xa2de08 -[_UISceneLifecycleMultiplexer uiScene:transitionedFromState:withTransitionContext:]
17 UIKitCore                      0xa39288 __186-[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]_block_invoke
18 UIKitCore                      0xeabec4 +[BSAnimationSettings(UIKit) tryAnimatingWithSettings:fromCurrentState:actions:completion:]
19 UIKitCore                      0xd9cc8 _UISceneSettingsDiffActionPerformChangesWithTransitionContextAndCompletion
20 UIKitCore                      0xa38f84 -[_UIWindowSceneFBSSceneTransitionContextDrivenLifecycleSettingsDiffAction _performActionsForUIScene:withUpdatedFBSScene:settingsDiff:fromSettings:transitionContext:lifecycleActionType:]
21 UIKitCore                      0x8781e4 __64-[UIScene scene:didUpdateWithDiff:transitionContext:completion:]_block_invoke.218
22 UIKitCore                      0x877278 -[UIScene _emitSceneSettingsUpdateResponseForCompletion:afterSceneUpdateWork:]
23 UIKitCore                      0x877e50 -[UIScene scene:didUpdateWithDiff:transitionContext:completion:]
24 UIKitCore                      0x1424918 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:]
25 UIKitCore                      0xed4cb4 -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:]
26 FrontBoardServices             0x1e3ec __95-[FBSScene _callOutQueue_didCreateWithTransitionContext:alternativeCreationCallout:completion:]_block_invoke
27 FrontBoardServices             0x1e8a4 -[FBSScene _callOutQueue_maybeCoalesceClientSettingsUpdates:]
28 FrontBoardServices             0x1e204 -[FBSScene _callOutQueue_didCreateWithTransitionContext:alternativeCreationCallout:completion:]
29 FrontBoardServices             0x8cbcc __93-[FBSWorkspaceScenesClient _callOutQueue_sendDidCreateForScene:transitionContext:completion:]_block_invoke.349
30 FrontBoardServices             0x2bf64 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:]
31 FrontBoardServices             0x48e04 -[FBSWorkspaceScenesClient _callOutQueue_sendDidCreateForScene:transitionContext:completion:]
32 FrontBoardServices             0x4a768 __92-[FBSWorkspaceScenesClient createSceneWithIdentity:parameters:transitionContext:completion:]_block_invoke_2
33 FrontBoardServices             0x2bf64 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:]
34 libdispatch.dylib              0x1b7fc _dispatch_client_callout
35 libdispatch.dylib              0x6bb4 _dispatch_block_invoke_direct
36 BoardServices                  0x91d4 __BSSERVICEMAINRUNLOOPQUEUE_IS_CALLING_OUT_TO_A_BLOCK__
37 BoardServices                  0x9054 BSServiceMainRunLoopSourceHandler
38 CoreFoundation                 0x68f10 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__
39 CoreFoundation                 0x68e84 __CFRunLoopDoSource0
40 CoreFoundation                 0x46acc __CFRunLoopDoSources0
41 CoreFoundation                 0x1d6d8 __CFRunLoopRun
42 CoreFoundation                 0x1ca6c _CFRunLoopRunSpecificWithOptions
43 GraphicsServices               0x1498 GSEventRunModal
44 UIKitCore                      0x9ddf8 -[UIApplication _run]
45 UIKitCore                      0x46e54 UIApplicationMain
46 UIKitCore                      0x172938 -[UIScrollView contentInset]
47 Runner                         0xdcf0 main (AppDelegate.swift)
48 ???                            0x193592e28 (Manquant)
        
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
Waiting for another flutter command to release the startup lock...
[✓] Flutter (Channel stable, 3.38.7, on macOS 26.2 25C56 darwin-arm64, locale fr-FR) [1 159ms]
    • Flutter version 3.38.7 on channel stable at /Users/maxime_pontoire/fvm/versions/3.38.7
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 3b62efc2a3 (4 weeks ago), 2026-01-13 13:47:42 -0800
    • Engine revision 78fc3012e4
    • Dart version 3.10.7
    • DevTools version 2.51.1
    • Pub download mirror https://artifact.socrate.vsct.fr/artifactory/api/pub/all-pub
    • Feature flags: enable-web, enable-linux-desktop, enable-macos-desktop, enable-windows-desktop,
      enable-android, enable-ios, cli-animations, enable-native-assets, omit-legacy-version-file,
      enable-lldb-debugging

[✗] Android toolchain - develop for Android devices [1 105ms]
    ✗ Unable to locate Android SDK.
      Install Android Studio from: https://developer.android.com/studio/index.html
      On first launch it will assist you in installing the Android SDK components.
      (or visit https://flutter.dev/to/macos-android-setup for detailed instructions).
      If the Android SDK has been installed to a custom location, please use
      `flutter config --android-sdk` to update to that location.


[✓] Xcode - develop for iOS and macOS (Xcode 26.2) [2,3s]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 17C52
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [13ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Connected device (4 available) [6,5s]
    • eMxPi’s iPhone (wireless) (mobile) • 00008130-00063DDA2E04001C            • ios            • iOS
      26.3 23D127
    • iPhone + Watch (mobile)            • A2B07733-85AB-4812-BFD2-1822DB74E7CF • ios            •
      com.apple.CoreSimulator.SimRuntime.iOS-26-2 (simulator)
    • macOS (desktop)                    • macos                                • darwin-arm64   •
      macOS 26.2 25C56 darwin-arm64
    • Chrome (web)                       • chrome                               • web-javascript •
      Google Chrome 145.0.7632.46

[✓] Network resources [326ms]
    • All expected network resources are available.
```

</details>


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[iOS] Crash NSGenericException in FlutterPluginAppLifeCycleDelegate (mutation while enumeration) #182361

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[iOS] Crash NSGenericException in FlutterPluginAppLifeCycleDelegate (mutation while enumeration) #182361

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